1. Field of the Invention
The present invention relates to electronic printers and printing systems, and more particularly, to a method of storing information regarding the status of all features of jobs in the printing system, and providing such stored information held within the printing system when necessary to recommence printing after crash recovery. The invention also relates to a method of permitting sequential completion of the jobs in a printing system up to a job requiring a faulted feature, and to the nonsequential completion of a job or jobs in the event of operator intervention.
2. Description of the Related Art
In electronic reprographic printing systems, a document or series of documents comprising at least one print job are successively scanned. Upon scanning of the documents, image signals are obtained and electronically stored as electronic pages. The signals are then read out successively and transferred to a printer for the formation of the images on paper. Once a document is scanned, it can be printed any number of times or processed in any number of ways (e.g., words deleted or added; image magnified or reduced, etc.). If a plurality of documents comprise a job which is scanned, the processing or manipulation of the scanned documents can include deletion of one or more documents, reordering of the documents into a desired order, or addition of a previously or subsequently scanned document or documents. The printing or processing can be relatively synchronous with scanning, or asynchronous after scanning. If asynchronous, a time interval exists between scanning and printing or processing. The system can then accumulate a number of scanned jobs in the system memory for subsequent processing or printing. The order of the jobs to be printed may be different from the order of jobs as scanned depending on the priority of the jobs and the desires of the operator for increasing productivity or through-put and decreasing printer or scanner down-time.
Each job entered into the system is accompanied with its own unique set of job features, collectively called "sheet information", which is stored in a "job bank" A job may have from 1 to 250 job banks, because a new job bank is needed for every sheet which is different from the previous one (i.e., paper color, paper stock). For example, if a job has 200 sheets which alternate colors of paper every other sheet, the job will require 200 job banks. If a job has several originals, but only one type of paper is needed, the job will require 2 job banks: one for the start sheet and one for the end sheet. If a job has one original and 50 copies are needed, this job requires only one job bank. It is a function of the system's memory to hold this information regarding the features of the jobs it is requested to print until such job is completed. Job features include such things as size and type of paper, duplex vs. simplex, number of sets, destination of sets, whether the job is to be collated, stitched or bound, etc. Operation in an electronic reprographic system can be interrupted for a variety of reasons. The interruption can be the result of a scanner or printer fault, hardware or software faults, paper misfeed, intentional interruption, etc. Some faults may require immediate attention prior to the completion of any job; others may affect job features which may not be required for the completion of a specific job entered into the system. If a fault or combination of faults is sufficiently critical to interfere with the total functioning of the printing system, a crash occurs, requiring crash recovery. If the features of the jobs still active at the time of such crash are not kept within the system's memory, a crash will necessitate reentering all of the sheet information before the job can be completed.
The related art discloses printing systems which employ a system's memory for many diverse purposes. In the prior art, U.S. Pat. Nos. 4,375,916 and 4,588,282 to Levine disclose a photocopying machine having a detachable, portable optical reader capable of being carried about by a user for temporarily recording an image of a printed document to be copied or reproduced. This device also contains a visual display means of the transferred images, enabling the users to initially observe the images before hard copies are made.
U.S. Pat. No. 4,843,428 to Sugiura discloses a copying machine which enables a number of document images to be pre-stored in memory in such a manner that any one document image can be selected and copied.
U.S. Pat. No. 4,920,427 to Hirata discloses a facsimile apparatus wherein received image information is stored in an accumulator in case printing trouble is detected. Upon elimination of the printing trouble, the image information stored is read out and printed. This invention provides for a "holding" of such image information.
Methods of storing job information for the purpose of effecting crash recovery have also been described. U.S. Pat. No. 4,665,520 to Strom discloses a recovery system in a multiprocessor system wherein messages are used to track down a fault within the system. Each message is dependent on another message from another recovery unit to create an expected session sequence number. By comparing the actual session sequence number to the expected session sequence number, a fault can be thus detected.
U.S. Pat. No. 4,229,100 to Travis applies a recovery system wherein messages are built on one another to relay information regarding the number of copies actually processed so that they can be properly billed in the event of a jam.
U.S. Pat. No. 4,443,849 to Ohwada discloses an error recovery system for a multiprocessor system wherein a processor communicates status signals to another processor without using the main memory, and provides for a diagnostic system by reviewing the status signals.
U.S Pat. No. 4,521,847 to Ziehm discloses a control system for job recovery after a malfunction wherein important job characteristics are stored in a nonvolatile memory so that if a crash or jam occurs, all of the job information will be available for job recovery. Once job recovery is done, all of the job data will be reloaded into the appropriate location.
U.S. Pat. No. 4,697,266 to Finley discloses an asynchronous checkpointing system for error recovery for use with a database. An error recovery table is used by a program to constantly update the database during a program's operation to ensure that the status of the database is as current as possible. The error recovery tables are stored in memory when a fault or other problem occurs.